In some wireless communication systems, user equipments (UEs) wirelessly communicate with one or more base stations. A wireless communication from a UE to a base station is referred to as an uplink communication. A wireless communication from a base station to a UE is referred to as a downlink communication. Resources are required to perform uplink and downlink communications. For example, a base station may wirelessly transmit data to a UE in a downlink communication at a particular frequency for a particular duration of time. The frequency and time duration are examples of resources.
Time-frequency resources are allocated for communications between UEs and a base station. Multiple access occurs when more than one UE is scheduled on a set of time-frequency resources. Each UE uses a portion of the time-frequency resources to receive data from the base station in the case of a downlink communication, or to transmit data to the base station in the case of an uplink communication.
Wireless communications between the base station and the UEs may be performed by transmitting orthogonal frequency-division multiplexing (OFDM) symbols. The frequency spacing used between the subcarriers of an OFDM symbol is called the subcarrier spacing.
It may be desirable to have some level of alignment between OFDM symbols having different subcarrier spacings.